The present invention relates to a pneumatic tire, more particularly to a tread pattern capable of satisfying both of the mud performance and noise performance.
Pneumatic tires for 4WD vehicles for use on paved or public roads as well as off paved roads, e.g. sport-utility vehicles, pickup trucks and the like, are required to have a good mud performance capable of producing a large drive power on muddy roads and a good noise performance capable of generating less noise during running on the smooth and well-paved city streets and the like.
In Japanese Patent Application Publication No. 2004-058839 corresponding to US Patent Application Publication No. 2004-0020577-A1, in order to satisfy both of mud performance and noise performance, as shown in FIG. 6, the tire has shoulder land zones rs and middle land zones rm divided by shoulder main grooves gs and crown main grooves gc; the shoulder land zones rs are divided by shoulder lateral grooves ys into rows of shoulder blocks bs; the middle land zones rm are formed as circumferential ribs; and the middle land zone rm is provided with inclined middle outward slots c1 extending from the shoulder main groove gs toward the axially inside, and inclined middle inward slots c2 extending from the crown main groove gc toward the axially outside. Further, the shoulder lateral grooves ys include first shoulder lateral grooves ys1 and second shoulder lateral grooves ys2 having different groove widths. In the vicinity of the tread edge to which contributes to the mud performance, in order to improve the mud performance, the groove width WLo of the first shoulder lateral groove ys1 is set to be larger than the groove width WSo of the second shoulder lateral groove ys2. On the other hand, in the vicinity of the connections between the lateral grooves ys1 and ys2 and the crown main groove gc which contributes to the noise performance, the groove width WLi of the first shoulder lateral grooves ys1 is set to be closer to the groove width WSi of the second shoulder lateral grooves ys2 in order to decrease the groove volume and thereby improve the noise performance. Therefore, in comparison with the conventional tire, the total groove volume of the shoulder lateral grooves is decreased and thereby the noise performance can be improved, and at the same time, it is possible to maintain the mud performance nearly equal to that of the conventional tire. Thus, this prior art is directed to the improvement in the shoulder land zones, therefore, there is room for improvement.